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Getting the code:

• git clone https://github.com/scodella/BTagSFUtil

• include BTagSFUtil.C in your code

Class Usage:

• BTagSFUtil *BTagSF = new BTagSFUtil(MeasurementType, BTagAlgorithm, OperatingPoint, SystematicIndex);

  Where: MeasurementType is the type of measurement you want to use: "mujets" -> combined b-jets SFs from methods based on QCD samples "comb" -> combined b-jets SFs from QCD and ttbar datasets "comb" -> SFs for light jets BTagAlgorithm is the btag algorithm you want to use, ex: "CSV" OperatingPoint can be "Loose", "Medium" or "Tight" SystematicIndex +1 (-1) to scale up (down) the b-jets SF according to they total uncertainty +3 (-3) to scale up (down) the light-jets SF according to they total uncertainty Remember that these two uncertainties have to be treated as independet!

• When running over FastSim MC, the dataset has to be specified to retrive special correction factors:

  BTagSFUtil *BTagSF = new BTagSFUtil(MeasurementType, BTagAlgorithm, OperatingPoint, SystematicIndex, FastSimDataset);

    Where the supported FastSim datasets for 8 TeV are T1bbbb, T1tttt, T2, T2bb, T2bwm T2tt and T3w
    SystematicIndex for FastSim SFs follow the same code as above +/-10 
    e.g. to scale down the FastSim SF for light-jets by its uncertainty, set SystematicIndex to -13
        Note that for FastSim indepenent SFs for c-jets are used, with SystematicIndex +/-12
        Important: FastSim SF uncertainties should be treated as independet from standard SF ones
  

• To get the SF for a given jet:

  BTagSF->GetJetSF(JetFlavor, JetPt, JetEta);

• For applying the SF to a jet according to the "flip a coin" method:

  BTagSF->IsTagged(DiscriminatorValue, JetFlavor, JetPt, JetEta);

    Where: DiscriminatorValue is the value for the discriminant of your choise for the jet to which the SF has being applied
  

  Important note: the method IsTagged is designed in order to make a minimal use of absolute b-tag efficiencies. Nevertheless, when the SFs a re larger than 1, those efficiencies must be computed in the very MC samples on which the SFs have being applied. The BTagEfficiencies/*.C files provide the efficiencies for some ttbar samples for example purposes only.

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